An object of the present invention is an probe with a bar of piezoelectric elements for an ultrasound apparatus. It finds application more particularly in the medical field where echographic ultrasound apparatuses are used for diagnostic purposes to show internal tissue structures of human bodies examined. However, it can be implemented in other field once a problem of electrical connection has to be resolved between a piezoelectric element and the control circuits of a probe to which it belongs.
An echograph has, schematically, a generator of electrical signals and a transducer probe to apply a mechanical vibration corresponding to these signals in a medium to be examined. During stops in transmission, the probe may be used reversibly to receive acoustic signals back-reflected by the medium, and to convert these signals into electrical signals which are subsequently applied to reception and processing means. For various reasons, notably for questions of resolution of the image restored by an echograph, the frequency of the electrical-acoustic signal is high. For these same reasons, the probe consists of several transducer elements aligned with one another. Each transducer piezoelectric element has two metallizations, which are located on opposite faces of this element and which must be connected to the transmission-reception circuits of the echograph. The dimensions of these elements are small and cause difficulties in making the system of connection of the electrical signal to these elements.
It is known, notably from a European patent application No. 84 308 373.4 filed on 3rd December 1984, that the electrical signal can be applied or picked up at the terminals of each transducer element in soldering electrical connection tracks, supported by a flexible printed circuit, directly to the metallizations of the elements. Subsequently, the flexible printed circuits are folded towards the rear of the probe and, by various arrangements, the probe is furthermore curved to correspond to a particularly desired use for the exploration of the medium studied: by sector scanning. This solution has numerous drawbacks. For example, the electrical connections are distributed at hot points on one side of the bar and cold points on the other side. This increases problems of diaphony among elements in this bar. Furthermore, the elements are metallized on three of their contiguous surfaces, and two electrically independent metallizations, assigned to the two faces of the element, have to be prepared by making a saw mark in the piezoelectric crystal thus prepared. This saw mark is difficult. It was conceived to overcome these drawbacks by adding, to either side of the transducer element, a relay block continuously metallized on at least two of its adjacent faces. The relay block can then be electrically connected by one of its faces to one of the faces of the transducer element and by its other face to a printed circuit type of connection circuit. For this printed circuit, the problems of curvature of the bar no longer play a role since its connections can be made after the curvature of this bar.
An example of an embodiment of this type is shown in FIG. 1. It was then thought to connect the corresponding faces of the relay blocks and the elements by connecting wires. This micro-connection operation is, however, difficult to undertake. In the present invention, advantage has been taken of the fact that the piezoelectrical elements are covered with a transition blade. This blade enables the acoustic signal to be adapted to the medium to be studied. This blade has the specific feature herein of being metallized on its face which is before the piezoelectric element that it covers. Besides, this blade goes beyond the piezoelectric element and also covers the relay block used for the electrical connection. The electrical signals are then conducted simply from the printed circuit, to the relay block, to the metallization of the blade and then finally to the metallization of the piezoelectric element.
In one improvement of the invention, a layer of non-conductive bonder is used to ensure the mechanical-electrical continuity among the support, the element and the blade. Contrary to what might have been expected, the layer of non-conductive bonder does not form an insulating screen for the electrical connection. In effect, non-conductive bonders have the particular feature of being very fluid. They can therefore be used in very small thickness. In then using faults in the appearance of the metallizations, which give these metallizations a granulated appearance, it is possible, by exerting adequate pressure during the bonding of the parts by their metallized part, to obtain a hammering, a molecular interpretation between these metallization layers. In this way, the bonding between these layers may be considered to be a dispersal of a multitude of electrical bridges between the mechanical bonds caused by the presence of the bonder. In any case, bonding of the metallizations, by bonder which is conductive or not, has the advantage over solders of not causing any additional risk of loosening of these metallizations.
The invention therefore concerns a probe for an ultrasound apparatus of the type with a bar of piezoelectric elements, each element being inserted between a support and an acoustic transition blade and being metallized on its faces which are before the support and its blade, characterized in that the blade and/or the support include a facing metallization designed to be connected to the corresponding metallization of the element.